It's definitely Naruto... Ninjas always beat pirates in my book!
If I had to rank them it'd go like this:
Naruto- I can't wait for every Wednesday to read it! I get up at 5:30 so I can read it before work!
Bleach/Fairy Tail- right now I think I these two are about even for me.. I enjoy them both a lot!
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One Piece- I just don't like the art in this one at all!!
The only reason I've even read any of it is cause it's in Jump. So I read it cause it was there.

1. Fairy Tale: Better storyline, The characters in the show main or not have all either played key roles or had arc dedicated to them unlike its competitors.

2. History's Strongest Disciple Kenichi: almost the same reasons as Fairy tale, but funnier.

3. Bleach: I loved bleach up until the story went off track from the Kings Key to Aizen no longer seeking to open the get to the 4th dimension but instead becoming "G.O.D." , now we seem to be getting back on track.

4. Naruto: I love the action , but hate the drag out and the how things from naruto changed in shippuden and how characters that were so strong in the first series get no screen time, long winded arcs which are boring, lol or this one i love during the fourth ninja war. Kakashi vs. the seven swordsmen of the mist. Kakashi says " let me show you why they call me the copy ninja" * with a serious face* snap shot of mangetsu hozuki then bam..27 issues down the line...all seven swordsmen sealed and kakashi with less marks then he had when he was fighting them O.o holes in narutos story

They all have a great story line, but many people became antifans of Naruto and bleach because of the fans... I think Naruto is the best manga out of those choices, but all of them, other than fairy tail have had their time in the spotlight and should end soon, especially Naruto and Bleach.